Looking up the definition of an unknown word when you read a text is an important part of learning. However, like doing every other task, if you have to switch to do another one, then your performance will decrease at both. This is a well known effect of multitasking.
So I suppose that both the performance of looking up the word and the performance of comprehending the text after the resumption will decrease as well, compared to the performance when you do them separately. This seems to be even more true if you can't understand the word in ~3 seconds, i.e. the definition you found is abstruse. Take this definition of the word
ostentatious in Merriam – Webster:
marked by or fond of conspicuous or vainglorious and sometimes pretentious display
Now instead of understanding the initial unknown word, you have three more ones:
pretentious. This is crazy!
Anyway, is there any evidence to support the above hypothesis?
(Since you don't need to look up for the meanings of the unknown words when you know 98% of the vocabulary of the text used, I guess at this level your vocabulary coverage is below 98%)